The Inhibition of Liposaccharide Heptosyltransferase WaaC with Multivalent Glycosylated Fullerenes: A New Mode of Glycosyltransferase Inhibition

Abstract

L,d‐Heptosides (L‐glycero‐D‐manno‐heptopyranoses) are found in important bacterial glycolipids such as lipopolysaccharide (LPS), the biosynthesis of which is targeted for the development of novel antibacterial agents. This work describes the synthesis of a series of fullerene hexa‐adducts bearing 12 copies of peripheral sugars displaying the mannopyranose core structure of bacterial l,d‐heptoside. The multimers were assembled through an efficient copper‐catalyzed alkyne–azide cycloaddition reaction as the final step. The final fullerene sugar balls were assayed as inhibitors of heptosyltransferase WaaC, the glycosyltransferase catalyzing the incorporation of the first L‐heptose into LPS. Interestingly, the inhibition of the final molecules was found in the low micromolar range (IC₅₀=7–45 μM), whereas the corresponding monomeric glycosides displayed high micromolar to low millimolar inhibition levels (IC₅₀ always above 400 μM). When evaluated on a “per‐sugar” basis, these inhibition data showed that, in each case, the average affinity of a single glycoside of the fullerenes towards WaaC was significantly enhanced when displayed as a multimer, thus demonstrating an unexpected multivalent effect. To date, such a multivalent mode of inhibition had never been evidenced with glycosyltransferases.